1. Field of the Invention
The present invention relates to a tilt angle sensor and, more specifically, to a tilt angle sensor that is capable of measuring a tilt angle, acceleration, and the like at least in one direction.
2. Description of the Related Art
In order to detect an action and a tilt of a prescribed object, it has conventionally been investigated to utilize an acceleration sensor that detects the acceleration of the object. For example, the acceleration sensor can be utilized to: detect a tilt to find out whether or not a camera is being held properly at the time of pressing a shutter release; detect a tilt of a motorbike for preventing it from falling down; detect a tilt of an electronic equipment, which indicates the loaded state, e.g., whether or not it is placed horizontally; and so on. Further, the acceleration sensor can also be utilized to detect forcible shifting or falling of an electronic equipment instantly so as to take a security measure on a movable part.
Regarding the structure of an acceleration sensor according to a conventional case, as disclosed in Patent Document 1, for example, there is employed a method for detecting a strain generated in a structural unit due to acceleration. Specifically, a weight is provided at the center (intersection point) of a cross-shaped supporting member that has a spring characteristic, and a distortion detecting element is fixedly provided at each beam part of the supporting member. Deformation of each beam is detected based on detection values from the distortion detecting elements so as to detect the acceleration in directions of each of axes (X, Y, and Z). For example, there are following methods to detect acceleration. That is, acceleration may be detected by forming a bridge circuit to detect a resistance value of a semiconductor piezoelectric element that is utilized as the distortion detecting element, or by detecting a transmitting cycle according to distortion by utilizing a piezoelectric vibrator as depicted in Patent Document 1.
Further, as a tilt sensor for detecting a tilt of a device, there is also such a type that is disclosed in Patent Document 2. This tilt sensor comprises a magnet and a pendulum, and it is structured to detect changes in magnetic field directions caused due to changes in the position of the pendulum by using a Hall element. More specifically, the pendulum to which a ferromagnet is mounted is pivotally supported to a case, and a tilt is detected by detecting changes in the magnetic field of the ferromagnet mounted to the pendulum that is rotated in accordance with a rotary action of the case by using a Hall IC.    Patent Document 1: Japanese Registered Patent Publication No. 2732287    Patent Document 2: Japanese Unexamined Patent Publication 2006-90796
However, the sensors disclosed in Patent Documents mentioned above have following inconveniences. First, for the sensor disclosed in Patent Document 1, it is necessary to provide electrodes at the cross-shaped supporting member (spring) and the vicinity thereof to be used for capturing signals for detecting distortion. Thus, it is possible that the structure thereof becomes complicated because of the wirings. Further, since the distortion detecting elements are mounted to the supporting member, the size cannot be reduced. Furthermore, the distortion detecting elements are mounted or built-in to the spring part of the supporting member, which disturbs displacement of the spring and makes it difficult to detect distortion with high sensitivity.
Further, the sensor disclosed in Patent Document 2 uses the pendulum, so that it is difficult to reduce the size. Furthermore, when there is oscillation generated in the pendulum, it is difficult to resolve continuation of the oscillation in a short time. Especially, oscillation is generated also by a noise that induces oscillation of the pendulum, and such oscillation continues for a long time. If so, a tilt angle and acceleration cannot be detected while the oscillation is continuing, so that the quality as a sensor cannot be improved.